Academic Commons Search Resultshttp://academiccommons.columbia.edu/catalog.rss?f%5Bsubject_facet%5D%5B%5D=Astronomy&q=&rows=500&sort=record_creation_date+desc
Academic Commons Search Resultsen-usHigh Energy Studies of Astrophysical Dusthttp://academiccommons.columbia.edu/catalog/ac:179736
Corrales, Lia Racquelhttp://dx.doi.org/10.7916/D85T3J69Tue, 18 Nov 2014 00:00:00 +0000Astrophysical dust -- any condensed matter ranging from tens of atoms to micron sized grains -- accounts for about one third of the heavy elements produced in stars and disseminated into space. These tiny pollutants are responsible for producing the mottled appearance in the spray of light we call the "Milky Way." However these seemingly inert particles play a strong role in the physics of the interstellar medium, aiding star and planet formation, and perhaps helping to guide galaxy evolution. Most dust grains are transparent to X-ray light, leaving a signature of atomic absorption, but also scattering the light over small angles. Bright X-ray objects serendipitously situated behind large columns of dust and gas provide a unique opportunity to study the dust along the line of sight. I focus primarily on X-ray scattering through dust, which produces a diffuse halo image around a central point source. Such objects have been observed around X-ray bright Galactic binaries and extragalactic objects that happen to shine through the plane of the Milky Way. I use the Chandra X-ray Observatory, a space-based laboratory operated by NASA, which has imaging resolution ideal for studying X-ray scattering halos. I examine several bright X-ray objects with dust-free sight lines to test their viability as templates and develop a parametric model for the Chandra HETG point spread function (PSF).Astrophysics, Astronomy, Physicslrc2123AstronomyDissertationsFIREBall, CHAS, and the diffuse universehttp://academiccommons.columbia.edu/catalog/ac:177160
Hamden, Erikahttp://dx.doi.org/10.7916/D8Z31WZFMon, 25 Aug 2014 00:00:00 +0000The diffuse universe, consisting of baryons that have not yet collapsed into structures such as stars, galaxies, etc., has not been well studied. While the intergalactic and circumgalactic mediums (IGM & CGM) may contain 30-40% of the baryons in the universe, this low density gas is difficult to observe. Yet it is likely a key driver of the evolution of galaxies and star formation through cosmic time. The IGM provides a reservoir of gas that can be used for star formation, if it is able to accrete onto a galaxy. The CGM bridges the IGM and the galaxy itself, as a region of both inflows from the IGM and outflows from galactic star formation and feedback. The diffuse interstellar medium (ISM) gas and dust in the galaxy itself may also be affected by the CGM of the galaxy. Careful observations of the ISM of our own Galaxy may provide evidence of interaction with the CGM. These three regions of low density, the IGM, CGM, and ISM, are arbitrary divisions of a continuous flow of low density material into and out of galaxies. My thesis focuses on observations of this low density material using existing telescopes as well as on the development of technology and instruments that will increase the sensitivity of future missions. I used data from the Galaxy Evolution Explorer (GALEX) to create an all sky map of the diffuse Galactic far ultraviolet (FUV) background, probing the ISM of our own galaxy and comparing to other Galactic all sky maps. The FUV background is primarily due to dust scattered starlight from bright stars in the Galactic plane, and the changing intensity across the sky can be used to characterize dust scattering asymmetry and albedo. We measure a consistent low level non-scattered isotropic component to the diffuse FUV, which may be due in small part to an extragalactic component. There are also several regions of unusually high FUV intensity given other Galactic quantities. Such regions may be the location of interactions between Galactic super-bubbles and the CGM. Other ways of probing the CGM including direct detection via emission lines. I built a proto-type of the Circumgalactic Hα Spectrograph (CHαS), a wide-field, low-cost, narrow-band integral field unit (IFU) that is designed to observe Hα emission from the CGM of nearby, low-z galaxies. This proto-type has had two recent science runs, with preliminary data on several nearby galaxies. Additional probes of the CGM are emission lines in the rest ultra-violet. These include OVI, Lyα, CIV, SiIII, CIII, CII, FeII, and MgII. Such lines are accessible for low redshift galaxies in the space UV, historically a difficult wavelength range in which to work due in part to low efficiency of the available detectors. I have worked with NASA's Jet Propulsion Laboratory to develop advanced anti-reflection (AR) coatings for use on thinned, delta-doped charge coupled device (CCD) detectors. These detectors have achieved world record quantum efficiency (QE) at UV wavelengths (> 50% between 130 nm and 300nm), with the potential for even greater QE with a more complex coating. One of these AR coated detectors will be used on the Faint Intergalactic Redshifted Emission Balloon (FIREBall-2), a balloon-born UV spectrograph designed to observe the CGM at 205 nm via redshifted Lyα (at z=0.7), CIV (at z=0.3), and OVI (at z=1.0). FIREBall-2 will launch in the fall of 2015.Astronomyeth2101AstronomyDissertationsObserving and Modeling the Optical Counterparts of Short-Period Binary Millisecond Pulsars.http://academiccommons.columbia.edu/catalog/ac:177121
Schroeder, Joshuahttp://dx.doi.org/10.7916/D8BC3WRPTue, 12 Aug 2014 00:00:00 +0000In this dissertation, I explore the subject of short-period binary millisecond pulsars discovered by the Fermi Gamma-ray Space Telescope and radio follow-up teams, and present observations of fields containing eight recently discovered short-period (Porb < 1 d) binary millisecond pulsars using the telescopes at MDM Observatory. The goal of these observations was to detect the optical counterparts of the binaries and, for the best-suited counterparts detected, to observe the photometric variation of the companion that happens over the course of the orbit in various filters. The hope was to then use the light curves to model the systems and obtain constraints on the mass of the neutron stars which are likely to be some of the most massive neutron stars in the galaxy. Optical counterparts to four of these systems are detected, one of which, PSR J2214+3000, is a novel detection. Additionally, I present the fully orbital phase-resolved B, V , and R light curves of the optical counterparts to two objects, PSR J1810+1744 and PSR J2215+5135, for which I employ the ELC model of Orosz & Hauschildt (2000) to measure the unknown system parameters. For PSR J1810+1744 I find that the system parameters cannot be fit even assuming that 100% of the spin-down luminosity of the pulsar is irradiating the secondary, and so radial velocity measurements of this object will be required for the complete solution. However, PSR J2215+5135 exhibits light curves that are extremely well constrained using the ELC model and we find that the mass of the neutron star is constrained by these and the radio observations to be MNS > 1.75 solar masses; at the 3-sigma level. I also find a discrepancy between the model temperature and the measured colors of this object which I interpret as possible evidence for an additional high-temperature source such as a quiescent disk. Given this and the fact that PSR J2215+5135 contains a relatively high mass companion (Mc > 0.1 solar masses), I propose that similar to the binary pulsar systems PSR J1023+0038 and IGR J18245-2452, the pulsar may transition between accretion- and rotation-powered modes.Astronomyjps2143AstronomyDissertationsThe Role of Cold Gas in Massive Galaxy Evolutionhttp://academiccommons.columbia.edu/catalog/ac:176912
Lemonias, Jennahttp://dx.doi.org/10.7916/D8CC0XVMMon, 07 Jul 2014 00:00:00 +0000The cold gas content of a galaxy reflects its past assembly history as well as its potential for future star formation. It has been shown to be tied to a galaxy's morphology, current star formation rate, and environment. In combination with large surveys at optical and ultraviolet wavelengths, measurements of the cold gas in galaxies provide new ways of understanding and examining the complex relationship between cold gas and derived quantities related to structural and star-forming properties. In particular, measurements of the cold gas content of galaxies can help inform the interpretation of global scaling relations in the local population of galaxies that cannot be fully understood without knowledge of the gas content of galaxies. However, the long integration times required to detect neutral hydrogen gas (HI) and CO make it difficult to detect low levels of cold gas in large numbers of galaxies. Where the presence of cold gas is assumed to be important but observations are not available, we can sometimes make assumptions to estimate the precise role of cold gas. With the advent of large surveys measuring cold gas in representative samples of galaxies, we have been able to study the cold gas in galaxies in a statistical way that rivals the methods by which we can study other properties of galaxies. In this thesis we use measurements from GALEX, SDSS, and the GALEX Arecibo SDSS Survey (GASS; Catinella et al. 2010) to quantitatively describe the distribution of cold gas in massive galaxies using sophisticated techinques that had previously only been applied to quantities derived from optical and ultraviolet observations. We also show how we can use distribution functions derived from large surveys to identify galaxies in distinct evolutionary phases that can shed light on the processes of galaxy evolution in general, and more specifically, about the crucial role HI plays in driving the evolution of massive galaxies. In Chapter 2 we design a classification scheme to identify galaxies with unexpected star formation in their outer disks (extended ultraviolet, or XUV, disks) and to extend the known sample of such objects out to moderate (z~0.05) redshifts. We find that 20% of galaxies in the most nearby portion of the sample exhibit XUV-disks and that XUV-disks are surprisingly common in massive, bulge-dominated galaxies. From our large, unbiased sample of galaxies we derive the space density of XUV-disks in the local universe. With this derived space density, and based on the assumption that XUV-disks must form in extended cold gas disks, we estimate the cold gas accretion rate onto XUV-disks in the local universe. In Chapter 3 we derive the bivarate HI-stellar mass function for massive galaxies, which is a crucial tool for constraining simulations. We test six different parameterizations of the distribution function and we also examine how the shape of the distribution function depends on star formation rate. We find that the location of the peak in the distribution function does not depend strongly on stellar mass or star formation rate but that the slope of the distribution function at low masses does. We also discuss how physical processes drive the shape of the bivariate HI-stellar mass function. Finally, in Chapter 4 we demonstrate the utility of scaling relations derived from large datasets by using the gas fraction scaling relation to select an anomalous sample of massive HI-rich galaxies with surprisingly low levels of star formation. We obtain HI imaging of these galaxies to ascertain why so much of their cold gas content is not participating in star formation. All of the galaxies we observe exhibit extended HI disks whose gas surface densities are below the threshold required for star formation. Since this type of galaxy is most prevalent at stellar masses above the transition mass noted in Kauffmann et al. (2003), it is possible that the processes inhibiting star formation in these galaxies contribute to the change in star-forming properties above the transition mass.Astronomy, Astrophysicsjjl2148AstronomyDissertationsUnderstanding the Nature of Stellar Chemical Abundance Distributions in Nearby Stellar Systemshttp://academiccommons.columbia.edu/catalog/ac:173510
Lee, Duane Morrishttp://dx.doi.org/10.7916/D84747X6Fri, 25 Apr 2014 00:00:00 +0000Since stars retain signatures of their galactic origins in their chemical compositions, we can exploit the chemical abundance distributions that we observe in stellar systems to put constraints on the nature of their progenitors. In this thesis, I present results from three projects aimed at understanding how high resolution spectroscopic observations of nearby stellar systems might be interpreted. The first project presents one possible explanation for the origin of peculiar abundance distributions observed in ultra-faint dwarf satellites of the Milky Way. The second project explores to what extent the distribution of chemical elements in the stellar halo can be used to trace Galactic accretion history from the birth of the Galaxy to the present day. Finally, a third project focuses on developing an input optimization algorithm for the second project to produce better estimates of halo accretion histories. In conclusion, I propose some other new ways to use statistical models and techniques along with chemical abundance distribution data to uncover galactic histories.Astronomy, Statistics, Nuclear chemistryAstronomyDissertationsFound: the progenitors of AM CVn and supernovae .Iahttp://academiccommons.columbia.edu/catalog/ac:171962
Kilic, Mukremin; Hermes, J.J.; Gianninas, A.; Brown, Warren R.; Heinke, Craig O.; Agueros, Marcel; , Paul Chote; Sullivan, Denis J. ; Bell, Keaton J. ; Harrold, Samuel T. http://dx.doi.org/10.7916/D8NS0RX2Tue, 25 Mar 2014 00:00:00 +0000We present optical and X-ray observations of two tidally distorted, extremely low-mass white dwarfs (WDs) with massive companions. There is no evidence of neutron stars in our Chandra and XMM observations of these objects. SDSS J075141.18−014120.9 (J0751) is an eclipsing double WD binary containing a 0.19 M⊙ WD with a 0.97 M⊙ companion in a 1.9 h orbit. J0751 becomes the fifth eclipsing double WD system currently known. SDSS J174140.49+652638.7 (J1741) is another binary containing a 0.17 M⊙ WD with an unseen M ≥ 1.11 M⊙ WD companion in a 1.5-h orbit. With a mass ratio of ≈0.1, J1741 will have stable mass transfer through an accretion disc and turn into an interacting AM Canum Venaticorum (AM CVn) system in the next ≈160 Myr. With a mass ratio of 0.2, J0751 is likely to follow a similar evolutionary path. These are the first known AM CVn progenitor binary systems and they provide important constraints on the initial conditions for AM CVn. Theoretical studies suggest that both J0751 and J1741 may create thermonuclear supernovae in ∼10^8 yr, either .Ia or Ia. Such explosions can account for ∼1 per cent of the Type Ia supernova rate.Astronomymaa17Astronomy and AstrophysicsArticlesThe bulk expansion of the supernova remnant Cassiopeia A at 151 MHzhttp://academiccommons.columbia.edu/catalog/ac:171995
Agueros, Marcel; Green, D.A.http://dx.doi.org/10.7916/D88G8HRFTue, 25 Mar 2014 00:00:00 +0000We present observations of the supernova remnant Cassiopeia A made over 13 yr at 151 MHz with the Cambridge Low-Frequency Synthesis Telescope. These observations have been used to study the contraction of well-defined minima in the visibility (or u,v) plane, in order to determine the bulk expansion of the radio emission from Cas A. These observations show steady contraction of the first and second minima, corresponding to expansion time-scales of ∼ 400–500 yr. These time-scales are less than those inferred from the expansion of compact radio knots in Cas A, and imply, provided that shape changes are not significant, that the remnant is in the transition between free expansion and Sedov-Taylor phases.Astronomymaa17Astronomy and AstrophysicsArticlesEmployment and Funding in Astronomyhttp://academiccommons.columbia.edu/catalog/ac:172004
Seth, Anil; Agueros, Marcel; Covey, Kevin; Danner, Rolf; Jang-Condell, Hannah; Metcalfe, Travis; Modjaz, Maryam; Rasio, Fred; Redfield, Seth; Sheth, Kartik; Waller, William ; West, Andrew ; Yoachim, Peterhttp://dx.doi.org/10.7916/D8RJ4GHDTue, 25 Mar 2014 00:00:00 +0000Astronomymaa17Astronomy and AstrophysicsWorking papersPanchromatic properties of 99 000 galaxies detected by SDSS, and (some by) ROSAT, GALEX, 2MASS, IRAS, GB6, FIRST, NVSS and WENSS surveyshttp://academiccommons.columbia.edu/catalog/ac:171983
Obric, M.; Ivezic, Z. ; Best, P.N. ; Lupton, R.H. ; Tremonti, C. ; Brinchmann, J.; Agueros, Marcel; Knapp, G.R.; Gunn, J.E. ; Rockosi, C.M.; Schlegel, D.; Finkbeiner, D.; Gacesa, M.; , V. Smolcic; Anderson, S.F.; Voges, W.; Juric, M.; Siverd, R.J.; Steinhardt, W. ; Jagoda, A.S.; Blanton, M.R.; Schneider, D.P.http://dx.doi.org/10.7916/D8J1016FTue, 25 Mar 2014 00:00:00 +0000We discuss the panchromatic properties of 99 088 galaxies selected from the Sloan Digital Sky Survey (SDSS) Data Release 1 ‘main’ spectroscopic sample (a flux-limited sample for 1360 deg^2). These galaxies are positionally matched to sources detected by ROSAT, Galaxy Evolution Explorer (GALEX), two-Micron All-Sky Survey (2MASS), Infrared Astronomical Satellite (IRAS), Green Bank GB6 survey (GB6), Faint Images of the Radio Sky at Twenty-centimetres (FIRST), NRAO VLA Sky Survey (NVSS) and Westerbork Northern Sky Survey (WENSS). The matching fraction varies from less than 1 per cent for ROSAT and GB6 to ∼40 per cent for GALEX and 2MASS. In addition to its size, the advantages of this sample are well-controlled selection effects, faint flux limits and the wealth of measured parameters, including accurate X-ray to radio photometry, angular sizes and optical spectra. We find strong correlations between the detection fraction at other wavelengths and optical properties such as flux, colours and emission-line strengths. For example, ∼2/3 of SDSS ‘main’ galaxies classified as active galactic nucleus (AGN) using emission-line strengths are detected by 2MASS, while the corresponding fraction for star-forming galaxies (SFs) is only ∼1/10. Similarly, over 90 per cent of galaxies detected by IRAS display strong emission lines in their optical spectra, compared to ∼50 per cent for the whole SDSS sample. Using GALEX, SDSS and 2MASS data, we construct the ultraviolet–infrared (UV–IR) broad-band spectral energy distributions for various types of galaxies, and find that they form a nearly one-parameter family. For example, the SDSS u- and r-band data, supplemented with redshift, can be used to ‘predict’ K-band magnitudes measured by 2MASS with an rms scatter of only 0.2 mag. When a dust content estimate determined from SDSS spectra with the aid of models is also utilized, this scatter decreases to 0.1 mag and can be fully accounted for by measurement uncertainties. We demonstrate that this interstellar dust content, inferred from optical SDSS spectra by Kauffmann et al., is indeed higher for galaxies detected by IRAS and that it can be used to ‘predict’ measured IRAS 60 μm flux density within a factor of 2 using only SDSS data. We also show that the position of a galaxy in the emission-line-based Baldwin–Phillips–Terlevich diagram is correlated with the optical light concentration index and u−r colour determined from the SDSS broad-band imaging data, and discuss changes in the morphology of this diagram induced by requiring detections at other wavelengths. Notably, we find that SDSS ‘main’ galaxies detected by GALEX include a non-negligible fraction (10–30 per cent) of AGNs, and hence do not represent a clean sample of starburst galaxies. We study the IR–radio correlation and find evidence that its slope may be different for AGN and SFs and related to the Hα/Hβ line-strength ratio.Astronomymaa17Astronomy and AstrophysicsArticlesThe runaway binary LP 400−22 is leaving the Galaxyhttp://academiccommons.columbia.edu/catalog/ac:171998
Kilic, Mukremin; Gianninas, A. ; Brown, Warren R. ; Harris, Hugh C.; Dahn, Conard C.; Agueros, Marcel; Heinke, Craig O. ; Kenyon, S.J.; Panei, J.A.; Camilo, Fernando http://dx.doi.org/10.7916/D84Q7S2KTue, 25 Mar 2014 00:00:00 +0000We present optical spectroscopy, astrometry, radio and X-ray observations of the runaway binary LP 400−22. We refine the orbital parameters of the system based on our new radial velocity observations. Our parallax data indicate that LP 400−22 is significantly more distant (3σ lower limit of 840 pc) than initially predicted. LP 400−22 has a tangential velocity in excess of 830 km s^−1; it is unbound to the Galaxy. Our radio and X-ray observations fail to detect a recycled millisecond pulsar companion, indicating that LP 400−22 is a double white dwarf system. This essentially rules out a supernova runaway ejection mechanism. Based on its orbit, a Galactic Centre origin is also unlikely. However, its orbit intersects the locations of several globular clusters; dynamical interactions between LP 400−22 and other binary stars or a central black hole in a dense cluster could explain the origin of this unusual binary.Astronomymaa17Astronomy and AstrophysicsArticlesThe Behavior of Matter under Extreme Conditionshttp://academiccommons.columbia.edu/catalog/ac:172001
Paerels, Frederik B.; Mendez, M.; Agueros, Marcel; Baring, M. ; Barret, D. ; Bhattacharyya, S.; Cackett, E.; Cottam, J. ; Diaz Tringo, M. ; Fox, D. ; Garcia, M. ; Gotthelf, Eric V.; Hermsen, W.; Ho, W. ; Hurley, K. ; Jonker, P.; Juett, A.; Kaaret, P.; Kargaltsev, O.; Lattimer, J. ; Matt, G.; Ozel, F. ; Pavlov, G.; Rutledge, R. ; Smith, R. ; Stella, L. ; Strohmayer, T.; Tananbaum, H.; Uttley, P.; van Kerkwijk, M.; Weisskopf, M. ; Zane, S. http://dx.doi.org/10.7916/D8125QPKTue, 25 Mar 2014 00:00:00 +0000The cores of neutron stars harbor the highest matter densities known to occur in nature, up to several times the densities in atomic nuclei. Similarly, magnetic field strengths can exceed the strongest fields generated in terrestrial laboratories by ten orders of magnitude. Hyperon-dominated matter, deconfined quark matter, superfluidity, even superconductivity are predicted in neutron stars. Similarly, quantum electrodynamics predicts that in strong magnetic fields the vacuum becomes birefringent. The properties of matter under such conditions is governed by Quantum Chromodynamics (QCD) and Quantum Electrodynamics (QED), and the close study of the properties of neutron stars offers the unique opportunity to test and explore the richness of QCD and QED in a regime that is utterly beyond the reach of terrestrial experiments. Experimentally, this is almost virgin territory.Astronomy, Astrophysicsfbp4, maa17, eg308Astronomy and AstrophysicsWorking papersNonlinear Data Assimilation: Towards a Prediction of the Solar Cyclehttp://academiccommons.columbia.edu/catalog/ac:171928
Svedin, Andreashttp://dx.doi.org/10.7916/D8TH8JR5Thu, 20 Mar 2014 00:00:00 +0000The solar cycle is the cyclic variation of solar activity, with a span of 9-14 years. The prediction of the solar cycle is an important and unsolved problem with implications for communications, aviation and other aspects of our high-tech society. Our interest is model-based prediction, and we present a self-consistent procedure for parameter estimation and model state estimation, even when only one of several model variables can be observed. Data assimilation is the art of comparing, combining and transferring observed data into a mathematical model or computer simulation. We use the 3DVAR methodology, based on the notion of least squares, to present an implementation of a traditional data assimilation. Using the Shadowing Filter - a recently developed method for nonlinear data assimilation - we outline a path towards model based prediction of the solar cycle. To achieve this end we solve a number of methodological challenges related to unobserved variables. We also provide a new framework for interpretation that can guide future predictions of the Sun and other astrophysical objects.Astronomy, Astrophysics, Applied mathematicsaos2112AstronomyDissertationsGas around Galaxies and Cluster: The Case for the Virgo Clusterhttp://academiccommons.columbia.edu/catalog/ac:171209
Yoon, Joo Heonhttp://dx.doi.org/10.7916/D8NK3C2CFri, 28 Feb 2014 00:00:00 +0000The presence of warm (T<10<super>5</super> K) and cold (T<10<super>4</super> K) gas and the dependence of its properties on environment are investigated in this thesis. Gas is a fundamental source of fuel for stars and galaxies and therefore it is an important tool for understanding galaxy evolution. We completed the first systematic survey of QSO absorption line observations in a galaxy cluster. In addition to these absorption line data, atomic hydrogen data of spiral galaxies in the Virgo Cluster are used to study (1) the distribution and flows of Ly&alpha absorbers, i.e., warm gas, in and around a galaxy cluster, (2) the effect of environment on the circumgalactic medium, and (3) the cause of neutral hydrogen gas extended beyond optical disks. Little warm gas is detected in the cluster center while there is abundant warm gas in the cluster outskirts and in the places where the Virgo substructures exist. The cluster is fully surrounded by low column density (N<sub>HI</sub> &sim 10<super>13</super> cm<super>-2</super>) warm gas. We conclude that it is infalling onto the cluster with the galaxies along the substructures. The galaxies in the substructures also have abundant cold gas. We are seeing the flows of gas and galaxies along filaments connected to the Virgo Cluster. The gas surrounding a galaxy, the circumgalactic medium, is mostly found for the galaxies in the circumcluster environment. The circumgalactic medium of galaxies close to the center of the cluster is truncated. Therefore, the cluster environment removes gas around a galaxy, which is a future source for continuing star formation. The atomic hydrogen observations of galaxies with extended HI disks are investigated to understand the its formation and connection of extended cold gas to environment. Galaxy-galaxy tidal interactions and gas accretion are the possible mechanisms to build up such gaseous disks. Throughout this thesis, we find gaseous filaments feeding galaxies and a cluster. The gas properties of galaxies, including the circumgalactic medium and extended disk gas, in and around the cluster show a strong dependence on environment.Astronomy, Astrophysicsjy2327AstronomyDissertationsCompact Galactic Neutral Hydrogen Clouds in the GALFA-HI Surveyhttp://academiccommons.columbia.edu/catalog/ac:168496
Saul, Destry Rosehttp://dx.doi.org/10.7916/D8PZ56SKMon, 06 Jan 2014 00:00:00 +0000The more sensitive the observations, the more complex the gas in our Galaxy appears. Since the detection of neutral hydrogen in 1951, each new survey has revealed new structure. Using the GALFA-HI survey, we have discovered five populations of compact neutral hydrogen clouds. We began by developing a machine-vision algorithm to identify compact clouds in the GALFA-HI Data Release 1. Based on position, velocity, and linewidth we separated the 1964 identified clouds into five populations: galaxy candidates, high-velocity clouds, cold low-velocity clouds, warm low-velocity clouds, and warm positive low-velocity clouds in the third Galactic quadrant. We found that the dust properties of the compact clouds support our population definitions. Using both IRAS and the newly released Planck data, we found no dust detections in the high-velocity clouds, or the warm positive low-velocity clouds in the third Galactic quadrant. We claim that the third quadrant clouds are low-velocity halo clouds. The warm low-velocity clouds have a significantly greater dust-to-gas ratio than the cold low-velocity clouds. We interpret this as evidence that the warm clouds have an ionized component not present with the cold clouds, possibly because they are part of the Galactic fountain.Astronomy, Astrophysicsdrs2125AstronomyDissertationsSample Palomar Transient Factory light curveshttp://academiccommons.columbia.edu/catalog/ac:167874
Price-Whelan, Adrian M.; Agueros, Marcel; Fournier, Amanda P.; Street, Rachel; Ofek, Eran O.; Covey, Kevin R.; Levitan, David; Laher, Russ R.; Sesar, Branimir; Surace, Jasonhttp://dx.doi.org/10.7916/D8CF9N1NMon, 25 Nov 2013 00:00:00 +0000These light curves are made available to the public as part of the publication of our recent paper, "Statistical Searches for Microlensing Events in Large, Non-Uniformly Sampled Time-Domain Surveys: A Test Using Palomar Transient Factory Data." We have selected ~10,000 light curves from the Palomar Transient Factory database that can be used to test the various statistical tools described in the paper.Astronomy, Statisticsmaa17AstronomyDatasetsExtreme Stellar Populations in the Universe: Backsplash Dwarf Galaxies and Wandering Starshttp://academiccommons.columbia.edu/catalog/ac:165921
Teyssier, Maureen Elizabethhttp://hdl.handle.net/10022/AC:P:21661Wed, 18 Sep 2013 00:00:00 +0000We demonstrate that stars beyond the virial radii of galaxies may be generated by the gravitational impulse received by a satellite as it passes through the pericenter of its orbit around its parent. These stars may become energetically unbound (escaped stars), or may travel to further than a few virial radii for longer than a few Gyr, but still remain energetically bound to the system (wandering stars). Larger satellites (10-100% the mass of the parent), and satellites on more radial orbits are responsible for the majority of this ejected population. Wandering stars could be observable on Mpc scales via classical novae, and on 100 Mpc scales via SNIa. The existence of such stars would imply a corresponding population of barely-bound, old, high velocity stars orbiting the Milky Way, generated by the same physical mechanism during the Galaxy's formation epoch. Sizes and properties of these combined populations should place some constraints on the orbits and masses of the progenitor objects from which they came, providing insight into the merging histories of galaxies in general and the Milky Way in particular. We distinguish between Local Group field galaxies which may have passed through the virial volume of the Milky Way, and those which have not, via a statistical comparison against populations of dark matter haloes in the Via Lactea II (VLII) simulation with known orbital histories. Analysis of VLII provides expectations for this escaped population: they contribute 13 per cent of the galactic population between 300 and 1500 kpc from the Milky Way, and hence we anticipate that about 7 of the 54 known Local Group galaxies in that distance range are likely to be Milky Way escapees. These objects can be of any mass below that of the Milky Way, and they are expected to have positive radial velocities with respect to the Milky Way. Comparison of the radius-velocity distributions of VLII populations and measurements of Local Group galaxies presents a strong likelihood that Tucana, Cetus, NGC3109, SextansA, SextansB, Antlia, NGC6822, Phoenix, LeoT, and NGC185 have passed through the Milky Way. Indeed, several of these galaxies -- especially those with lower masses -- contain signatures in their morphology, star formation history and/or gas content indicative of evolution seen in simulations of satellite/parent galactic interactions. Our results offer strong support for scenarios in which dwarfs of different types form a sequence in morphology and gas content, with evolution along the sequence being driven by interaction history. We use the Via Lactea II cosmological N-body simulation of the formation of Milky Way and M31 Analogues, to explore the expected properties of intergalactic light (light found beyond the virial radii of galaxies) in poor groups and around isolated galaxies. We find that the luminosity fraction of intergalactic light is ~1%. This is similar to observational measurements of intergalactic light in poor groups. We expect this result to be observationally verifiable through observations of supernovae Ia by blind, repeated surveys like Pan-STARRS and LSST. We find the major contributors to the intergalactic light are the largest mass satellite haloes due to the low stellar fraction expected in smaller mass haloes. The intergalactic light produced by the most massive satellites has a much smaller spatial extent than that produced by lower mass satellites, meaning that baryon prescriptions designed to supress star formation in low mass satellites also shrink the spatial extent of intergalactic light. It may be possible to use observations of the large quantity of intergalactic red giants, that we expect in the Local Group, to define the spatial extent of the intergalactic light, and thereby place limits on the total star formation in progenitor satellites in the Local Group.Astrophysics, Astronomymet2112AstronomyDissertationsInterstellar X-Ray Absorption Spectroscopy of Oxygen, Neon, and Iron with the Chandra LETGS Spectrum of X0614+091http://academiccommons.columbia.edu/catalog/ac:158176
Savin, Daniel Wolf; Kahn, S. M.; Paerels, Frederik B.; Brinkman, A. C.; Van der Meer, R. L. J; Kaastra, J. S.; Kuulkers, E.; Den Boggende, A. J. F.; Predehl, P.; Drake, Jeremy J.; Mclaughlin, Brendan M.http://hdl.handle.net/10022/AC:P:19462Mon, 25 Mar 2013 00:00:00 +0000We find resolved interstellar O K, Ne K, and Fe L absorption spectra in the Chandra X-Ray Observatory Low-Energy Transmission Grating Spectrometer (LETGS) spectrum of the low-mass X-ray binary X0614+091. We measure the column densities in O and Ne and find direct spectroscopic constraints on the chemical state of the interstellar O. These measurements probably probe a low-density line of sight through the Galaxy, and we discuss the results in the context of our knowledge of the properties of interstellar matter in regions between the spiral arms.Astrophysics, Astronomydws26, fbp4Astronomy and AstrophysicsArticlesNeutral Hydrogen in Local Group Dwarf Galaxieshttp://academiccommons.columbia.edu/catalog/ac:156128
Grcevich, Janahttp://hdl.handle.net/10022/AC:P:18909Mon, 04 Feb 2013 00:00:00 +0000The gas content of the faintest and lowest mass dwarf galaxies provide means to study the evolution of these unique objects. The evolutionary histories of low mass dwarf galaxies are interesting in their own right, but may also provide insight into fundamental cosmological problems. These include the nature of dark matter, the disagreement between the number of observed Local Group dwarf galaxies and that predicted by lambda cold dark matter models, and the discrepancy between the observed census of baryonic matter in the Milky Way's environment and theoretical predictions. This thesis explores these questions by studying the neutral hydrogen (HI) component of dwarf galaxies. First, limits on the HI mass of the ultra-faint dwarfs are presented, and the HI content of all Local Group dwarf galaxies is examined from an environmental standpoint. We find that those Local Group dwarfs within 270 kpc of a massive host galaxy are deficient in HI as compared to those at larger galactocentric distances. Ram-pressure arguments are invoked, which suggest halo densities greater than 0.0002-0.0003 per cubic centimeter out to distances of at least 70 kpc, values which are consistent with theoretical models and suggest the halo may harbor a large fraction of the host galaxy's baryons. We also find that accounting for the incompleteness of the dwarf galaxy count, known dwarf galaxies whose gas has been removed could have provided at most 210 million Solar Masses of HI gas to the Milky Way. Second, we examine the possibility of discovering unknown gas-rich ultra-faint galaxies in the Local Group using HI. The GALFA-HI Survey catalog is searched for compact, isolated HI clouds which are most similar to the expected HI characteristics of low mass dwarf galaxies. Fifty-one Local Group dwarf galaxy candidates are identified through column density, brightness temperature, and kinematic selection criteria, and their properties are explored. Third, we present hydrodynamic simulations of dwarf galaxies experiencing a constant velocity and density wind which emulates relative motion of the dwarf and the host's hot halo. These simulations resolve instabilities which can contribute to gas loss, such as the effects of the Kelvin Helmholtz instability. The results of these simulations support the hypothesis that rapid gas loss occurs when the ram pressure stripping criterion is met, with complete stripping occurs with a timescale of about half a Gyr. This stripping would occur in less than an orbital period for ultra-faint like dwarfs. Models which do not meet the ram-pressure stripping criterion show slower but constant mass loss which does not depend on the residual dwarf's gas mass. Extrapolating the stripping timescales, we show low-mass dwarf galaxies can be stripped on timescales between 1.1 and 3.3 Gyrs. These simulations are a first step towards accurate ram-pressure and dynamical mass loss rates for low mass Local Group galaxies orbiting within a hot halo. They suggest that the lack of low mass galaxies within 250 kpc of the Milky Way can be explained via ram-pressure and dynamical interactions between the satellite galaxy's gas and the hot halo.Astronomy, Astrophysicsjmg2223Astronomy and AstrophysicsDissertationsA Meshless Method for Magnetohydrodynamics and Applications to Protoplanetary Diskshttp://academiccommons.columbia.edu/catalog/ac:151776
McNally, Colin Powellhttp://hdl.handle.net/10022/AC:P:14425Fri, 17 Aug 2012 00:00:00 +0000This thesis presents an algorithm for simulating the equations of ideal magnetohydrodynamics and other systems of differential equations on an unstructured set of points represented by sample particles. Local, third-order, least-squares, polynomial interpolations (Moving Least Squares interpolations) are calculated from the field values of neighboring particles to obtain field values and spatial derivatives at the particle position. Field values and particle positions are advanced in time with a second order predictor-corrector scheme. The particles move with the fluid, so the time step is not limited by the Eulerian Courant-Friedrichs-Lewy condition. Full spatial adaptivity is implemented to ensure the particles fill the computational volume, which gives the algorithm substantial flexibility and power. A target resolution is specified for each point in space, with particles being added and deleted as needed to meet this target. Particle addition and deletion is based on a local void and clump detection algorithm. Dynamic artificial viscosity fields provide stability to the integration. The resulting algorithm provides a robust solution for modeling flows that require Lagrangian or adaptive discretizations to resolve. The code has been parallelized by adapting the framework provided by Gadget-2. A set of standard test problems, including one part in a million amplitude linear MHD waves, magnetized shock tubes, and Kelvin-Helmholtz instabilities are presented. Finally we demonstrate good agreement with analytic predictions of linear growth rates for magnetorotational instability in a cylindrical geometry. We provide a rigorous methodology for verifying a numerical method on two dimensional Kelvin-Helmholtz instability. The test problem was run in the Pencil Code, Athena, Enzo, NDSPHMHD, and Phurbas. A strict comparison, judgment, or ranking, between codes is beyond the scope of this work, although this work provides the mathematical framework needed for such a study. Nonetheless, how the test is posed circumvents the issues raised by tests starting from a sharp contact discontinuity yet it still shows the poor performance of Smoothed Particle Hydrodynamics. We then comment on the connection between this behavior and the underlying lack of zeroth-order consistency in Smoothed Particle Hydrodynamics interpolation. In astrophysical magnetohydrodynamics (MHD) and electrodynamics simulations, numerically enforcing the divergence free constraint on the magnetic field has been difficult. We observe that for point-based discretization, as used in finite-difference type and pseudo-spectral methods, the divergence free constraint can be satisfied entirely by a choice of interpolation used to define the derivatives of the magnetic field. As an example we demonstrate a new class of finite-difference type derivative operators on a regular grid which has the divergence free property. This principle clarifies the nature of magnetic monopole errors. The principles and techniques demonstrated in this chapter are particularly useful for the magnetic field, but can be applied to any vector field. Finally, we examine global zoom-in simulations of turbulent magnetorotationally unstable flow. We extract and analyze the high-current regions produced in the turbulent flow. Basic parameters of these regions are abstracted, and we build one dimensional models including non-ideal MHD, and radiative transfer. For sufficiently high temperatures, an instability resulting from the temperature dependence of the Ohmic resistivity is found. This instability concentrates current sheets, resulting in the possibility of rapid heating from temperatures on the order of 600 Kelvin to 2000 Kelvin in magnetorotationally turbulent regions of protoplanetary disks. This is a possible local mechanism for the melting of chondrules and the formation of other high-temperature materials in protoplanetary disks.Astronomy, Astrophysics, Mathematicscpm2118Astronomy and AstrophysicsDissertationsComparing Simulations and Observations of Galaxy Evolution: Methods for Constraining the Nature of Stellar Feedbackhttp://academiccommons.columbia.edu/catalog/ac:150614
Hummels, Cameron Brycehttp://hdl.handle.net/10022/AC:P:14229Tue, 24 Jul 2012 00:00:00 +0000Computational hydrodynamical simulations are a very useful tool for understanding how galaxies form and evolve over cosmological timescales not easily revealed through observations. However, they are only useful if they reproduce the sorts of galaxies that we see in the real universe. One of the ways in which simulations of this sort tend to fail is in the prescription of stellar feedback, the process by which nascent stars return material and energy to their immediate environments. Careful treatment of this interaction in subgrid models, so-called because they operate on scales below the resolution of the simulation, is crucial for the development of realistic galaxy models. Equally important is developing effective methods for comparing simulation data against observations to ensure galaxy models which mimic reality and inform us about natural phenomena. This thesis examines the formation and evolution of galaxies and the observable characteristics of the resulting systems. We employ extensive use of cosmological hydrodynamical simulations in order to simulate and interpret the evolution of massive spiral galaxies like our own Milky Way. First, we create a method for producing synthetic photometric images of grid-based hydrodynamical models for use in a direct comparison against observations in a variety of filter bands. We apply this method to a simulation of a cluster of galaxies to investigate the nature of the red-sequence/blue-cloud dichotomy in the galaxy color-magnitude diagram. Second, we implement several subgrid models governing the complex behavior of gas and stars on small scales in our galaxy models. Several numerical simulations are conducted with similar initial conditions, where we systematically vary the subgrid models, afterward assessing their efficacy through comparisons of their internal kinematics with observed systems. Third, we generate an additional method to compare observations with simulations, focusing on the tenuous circumgalactic medium. Informed by our previous studies, we investigate the sensitivity of this new mode of comparison to hydrodynamical subgrid prescription. Finally, we synthesize the results of these studies and identify future avenues of research.Astronomy, Astrophysicscbh2107Astronomy, Astronomy and AstrophysicsDissertationsWorking with Citizen Scientistshttp://academiccommons.columbia.edu/catalog/ac:150597
Hogg, David W.; Hunter, Jane; Bonney, Rick; Marx, Sabine M.http://hdl.handle.net/10022/AC:P:14224Tue, 24 Jul 2012 00:00:00 +0000Citizen scientists, members of the public who voluntarily contribute to scientific research projects, have informed research on protein-folding, discovered new celestial bodies, and tracked wildlife after last year's Gulf oil spill. In this discussion, the panelists share their experiences with citizen science initiatives and consider what factors contribute to a successful collaboration with interested amateurs. How have scientists created the necessary tools and infrastructure to gather data or verify analyses carried out by large numbers of citizen scientists? How do research funders and the scientific community view these projects? What does the future hold for citizen science? Panelists: David W. Hogg is an astronomer and physicist at New York University. One of the spin-offs of his research in observational cosmology, and in engineering systems that can manage and analyze enormous data sets, is Astrometry.net, a Web-based service that automatically calibrates amateur images of the sky for use in scientific investigations. Jane Hunter is a Professorial Research Fellow in the School of Information Technology and Electrical Engineering (ITEE) at the University of Queensland and the Director of the eResearch Lab where she leads a team developing software services for managing and analyzing scientific and research data. Rick Bonney is Director of Program Development and Evaluation at the Cornell Laboratory of Ornithology and a co-founder of the lab's citizen science program. Founder and director of www.citizenscience.org, he studies the impacts of public engagement in science.Information technology, Astronomy, Environmental science, Science educationsm2234Center for Research on Environmental Decisions, Scholarly Communication Program, Center for Digital Research and Scholarship, Libraries and Information ServicesInterviews and roundtablesGas in Void Galaxieshttp://academiccommons.columbia.edu/catalog/ac:141925
Kreckel, Kathryn Joycehttp://hdl.handle.net/10022/AC:P:11794Fri, 11 Nov 2011 00:00:00 +0000Void galaxies, residing within the deepest underdensities of the Cosmic Web, present an ideal population for the study of galaxy formation and evolution in an environment undisturbed by the complex processes modifying galaxies in clusters and groups, and provide an observational test for theories of cosmological structure formation. We investigate the neutral hydrogen properties (i.e. content, morphology, kinematics) of void galaxies, both individually and systematically, using a combination of observations and simulations, to form a more complete understanding of the nature of these systems. We investigate in detail the H I morphology and kinematics of two void galaxies. One is an isolated polar disk galaxy in a diffuse cosmological wall situated between two voids. The considerable gas mass and apparent lack of stars in the polar disk, coupled with the general underdensity of the environment, supports recent theories of cold flow accretion as an alternate formation mechanism for polar disk galaxies. We also examine KK 246, the only confirmed galaxy located within the nearby Tully Void. It is a dwarf galaxy with an extremely extended H I disk and signs of an H I cloud with anomalous velocity. It also exhibits clear misalignment between the kinematical major and minor axes, and a general misalignment between the H I and optical major axes. The relative isolation and extreme underdense environment make these both very interesting cases for examining the role of gas accretion in galaxy evolution. To study void galaxies as a population, we have carefully selected a sample of 60 galaxies that reside in the deepest underdensities of geometrically identified voids within the SDSS. We have imaged this new Void Galaxy Survey in H I at the Westerbork Synthesis Radio Telescope with a typical resolution of 8 kpc, probing a volume of 1.2 Mpc and 12,000 km s^-1 surrounding each galaxy. We reach H I mass limits of 2 x 10^8 M_sun and column density sensitivities of 5 x 10^19 cm^-2. We find that the void galaxies are generally gas rich, low luminosity, blue disk galaxies, but identify three as early type galaxies. The void galaxy optical and H I properties are not unusual for their luminosity and morphology. The small scale clustering in the void is similar to that in higher density regions, and we identify 18 H I rich neighboring galaxies in the voids. Two of these are systems of three galaxies linearly aligned and joined by a H I bridge, suggestive of filamentary formation within the void. We find no population of H I rich low luminosity galaxies within the observed voids that are not close companions of the targeted sample. Finally, to put these observations in a theoretical context, we analyze a (120 h^-1 Mpc)^3 adaptive mesh refinement hydrodynamic simulation that contains a high resolution subvolume centered on a ~30 Mpc diameter void. We construct mock observations with ~1 kpc resolution of the stellar and gas properties of these systems which reproduce the range of colors and luminosities observed in the SDSS for nearby galaxies, however we find no strong trends with density. We also make predictions for a significant population of low luminosity (M_r = -14) dwarf galaxies that is preferentially located in low density regions and specifically in the void center.Astronomyks2472Astronomy and AstrophysicsDissertationsMergers of Supermassive Black Hole Binaries in Gas-rich Environments: Models of Event Rates and Electromagnetic Signatureshttp://academiccommons.columbia.edu/catalog/ac:138452
Tanaka, Takamitsuhttp://hdl.handle.net/10022/AC:P:11117Fri, 09 Sep 2011 00:00:00 +0000Supermassive black holes permeate the observable Universe, residing in the nuclei of all or nearly all nearby massive galaxies and powering luminous quasars as far as ten billion light years away. These monstrous objects must grow through a combination of gas accretion and mergers of less massive black holes. The direct detection of the mergers by future gravitational-wave detectors will be a momentous scientific achievement, providing tests of general relativity and revealing the cosmic evolution of supermassive black holes. An additional -- and arguably equally rewarding -- challenge is the concomitant observation of merging supermassive black holes with both gravitational and electromagnetic waves. Such synergistic, "multi-messenger" studies can probe the expansion history of the Universe and shed light on the details of accretion astrophysics. This thesis examines the mergers of supermassive black hole binaries and the observable signatures of these events. First, we consider the formation scenarios for the earliest supermassive black holes. This investigation is motivated by the Sloan Digital Sky Survey observation of a quasar that appears to be powered by a supermassive black hole with a mass of billions of solar masses, already in place one billion years after the Big Bang. Second, we develop semianalytic, time-dependent models for the thermal emission from circumbinary gas disks around merging black holes. Our calculations corroborate the qualitative conclusion of a previous study that for black hole mergers detectable by a space-based gravitational-wave observatory, a gas disk near the merger remnant may exhibit a dramatic brightening of soft X-rays on timescales of several years. Our results suggest that this "afterglow" may become detectable more quickly after the merger than previously estimated. Third, we investigate whether these afterglow episodes could be observed serendipitously by forthcoming wide-field, high-cadence electromagnetic surveys. Fourth, we introduce a new subset of time-dependent solutions for the standard equation describing thin, viscous Keplerian disks. Finally, we apply these solutions to model the electromagnetic emission of accretion disks around supermassive black hole binaries that may be detectable with precision pulsar timing.Astrophysics, Astronomytt2196Astronomy and AstrophysicsDissertationsHigh-Contrast Observations with an Integral Field Spectrographhttp://academiccommons.columbia.edu/catalog/ac:137572
Zimmerman, Neil Thomashttp://hdl.handle.net/10022/AC:P:10968Tue, 23 Aug 2011 00:00:00 +0000This thesis is comprised of work carried out during the commissioning phase of Project 1640, a combined coronagraph--integral field spectrograph for Palomar Observatory's adaptive optics-equipped 200'' Hale Telescope. I have divided my investigations into three chapters. First, I describe the data reduction pipeline software, which solves a number of data extraction and calibration challenges unique to this kind of instrument. In the second chapter, I demonstrate a novel method for faint companion discovery which takes advantage of the high-precision relative astrometry enabled by a pupil plane reticle grid. This tool, in combination with the spectrophotometric capability of the integral field spectrograph, reveal that the A5V star Alcor has a heretofore unknown M-dwarf companion. In my third chapter, I explore the suitability of combining the non-redundant aperture mask interferometry technique with an integral field spectrograph. In the proof-of-concept observation of the spectroscopic binary star Beta CrB, I retrieve the first near-infrared spectrum of its F-dwarf companion.Astronomyntz2101Astronomy and AstrophysicsDissertationsInvestigations in time and of space using the FIRST survey : radio source variability and the evolution of FR II quasarshttp://academiccommons.columbia.edu/catalog/ac:129621
Thyagarajan, Nithyanandanhttp://hdl.handle.net/10022/AC:P:9833Fri, 25 Feb 2011 00:00:00 +0000The FIRST survey covered ~ 10,000 deg2 of the sky over a decade, providing unprecedented levels of flux density sensitivity (~ 1 mJy) at 1.4 GHz, uniformity to within 15% (at ~ 0.15 mJy rms), 5".4 angular resolution, astrometric accuracy to better than 1" and has cataloged ≥ 800,000 sources. It has made enormous contributions to diverse scientific ends including such subjects as radio source populations, quasars, large-scale structure and clustering of radio sources, gravitational lensing, cosmology, etc. I present the motivation, analysis and results of two projects also intended to demonstrate the power and expand the scope of the FIRST survey's scientific reach. A comprehensive search for variable and transient radio sources has been conducted using the ~ 55,000 snapshot images of the FIRST survey. An analysis leading to the discovery of 1,651 variable and transient objects down to mJy levels over a wide range of timescales (few minutes to years) is presented. The multi-wavelength matching for counterparts reveals the diverse classes of objects exhibiting variability. Interestingly, ~ 60% of the objects in the sample have either no classified counterparts or no corresponding sources at any other wavelength and require multi-wavelength follow-up observations. I discuss these classes of variables and speculate on the identity of objects that lack multi-wavelength counterparts. Thus, the FIRST survey has yielded the largest sample by far of radio variables and transients to date to unprecedented levels of sensitivity and sky coverage and demonstrates the promise of future radio instruments which have transient-detection as one of their key science projects. For decades, radio astronomers have attempted to use double-lobed radio sources to constrain the angular size-redshift (θ − z) relation and to derive cosmological parameters therefrom. Most of the early attempts have, embarrassingly, shown general consistency with a static Euclidean universe rather than with Friedmann models. These earlier results can be attributed to a combination of selection effects, sample definition problems, and inconsistencies in analysis. However, some recent and more successful analyses have still failed to distinguish among different Friedmann models. A catalog of ~ 680 FR II quasars was constructed from the FIRST sources with redshifts taken from the SDSS spectroscopic QSO catalog and a similar sized sample from the SDSS photometric QSO catalog which are the largest quasar compilations to date. Using statistical analyses, no evidence for intrinsic evolution of sizes with redshift is found. A static Euclidean model for the universe is clearly ruled out. However, new degeneracies between parameters in the multi-dimensional χ2-surface are found which can only be resolved with additional, independent information. Notable differences are found between the spectroscopic and photometric samples raising questions about the nature and origin of these populations.Astronomy, Astrophysicsnt2128AstronomyDissertations